Most businesses, government agencies, schools and other organizations employ dedicated communications systems (also referred to herein as “networks”) that enable computers, servers, printers, facsimile machines, telephones, security cameras and the like to communicate with each other, through a private network, and with remote locations via a telecommunications service provider. Such communications system may be hard-wired through, for example, the walls and/or ceilings of a building using communications cables and connectors. Typically, the communications cables contain eight insulated conductors such as copper wires that are arranged as four differential twisted pairs of conductors. Each twisted pair may be used to transmit a separate differential communications signal. Individual communications connectors (which are also referred to herein as “connector ports”) such as RJ-45 style modular wall jacks are mounted in offices, conference rooms and other work areas throughout the building. The communications cables and any intervening connectors provide communications paths from the connector ports (e.g., modular wall jacks) in offices and other rooms, hallways and common areas of the building (referred to herein as “work area outlets”) to network equipment (e.g., network switches, servers, memory storage devices, etc.) that may be located in a computer room, telecommunications closet or the like. Communications cables from external telecommunication service providers may also terminate within the computer room or telecommunications closet.
A commercial data center is a facility that may be used to run the computer-based applications that handle the core electronic business and operational data of one or more organizations. The expansion of the Internet has also led to a growing need for a so-called “Internet data centers,” which are data centers that are used by online retailers, Internet portals, search engine companies and the like to provide large numbers of users simultaneous, secure, high-speed, fail-safe access to their web sites. Both types of data centers may host hundreds, thousands or even tens of thousands of servers, routers, memory storage systems and other associated equipment. In these data centers, fiber optic communications cables and/or communications cables that include four differential pairs of insulated conductive (e.g., copper) wires are typically used to provide a hard-wired communications system that interconnects the data center equipment.
As noted above, the communications cables and connectors in conductive wire-based communication systems that are installed in both office buildings and data centers usually include eight conductors that are arranged as four differential pairs of conductors. Such communications systems typically use RJ-45 plugs and jacks to ensure industry-wide compatibility. Pursuant to certain industry standards (e.g., the TIA/EIA-568-B.2-1 standard approved Jun. 20, 2002 by the Telecommunications Industry Association), the eight conductors in RJ-45 plug and jack connectors are aligned in a row in the connection region where the contacts of the plug mate with the contacts of the jack. FIG. 1 is a schematic view of the front portion of an RJ-45 jack that illustrates the pair arrangement and positions of the eight conductors in this connection region that are specified in the type B configuration of the TIA/EIA-568-B.2-1 standard, which is the most widely used configuration. As shown in FIG. 1, under the TIA/EIA 568 type B configuration, conductors 4 and 5 comprise differential pair 1, conductors 1 and 2 comprise differential pair 2, conductors 3 and 6 comprise differential pair 3, and conductors 7 and 8 comprise differential pair 4. Herein, a differential pair of conductors may be referred to simply as a “pair.”
In both office network and data center communications systems, the communications cables that are connected to end devices (e.g., network servers, memory storage devices, network switches, work area computers, printers, facsimile machines, telephones, etc.) may terminate into one or more communications patching systems that may simplify later connectivity changes. Typically, a communications patching system includes one or more “patch panels” that are mounted on equipment rack(s) or in cabinet(s), and a plurality of “patch cords” that are used to make interconnections between different pieces of equipment. As is known to those of skill in the art, a “patch cord” refers to a communications cable (e.g., a cable that includes four differential pairs of copper wires or a fiber optic cable) that has a connector such as, for example, an RJ-45 plug or a fiber optic connector, on at least one end thereof. A “patch panel” refers to an inter-connection device that includes a plurality (e.g., 24 or 48) of connector ports. Each connector port (e.g., an RJ-45 jack or a fiber optic adapter) on a patch panel may have a plug aperture on a front side thereof that is configured to receive the connector of a patch cord (e.g., an RJ-45 plug), and the back end of each connector port may be configured to receive a communications cable. With respect to RJ-45 connector ports, each communications cable is typically terminated into the back end of the RJ-45 connector port by terminating the eight conductive wires of the cable into corresponding insulation displacement contacts (“IDCs”) or other wire connection terminals of the connector port. Consequently, each RJ-45 connector port on a patch panel acts to connect the eight conductors of the patch cord that is plugged into the front side of the connector port with the corresponding eight conductors of the communications cable that is terminated into the back end of the connector port. The patching system may optionally include a variety of additional equipment such as rack managers, system managers and other devices that facilitate making and/or tracking patching connections.
In a typical office network, “horizontal” cables are used to connect each work area outlet (which typically are RJ-45 jacks) to the back end of a respective connector port (which also typically are RJ-45 jacks) on a first set of patch panels. The first end of each of these horizontal cables is terminated into the IDCs of a respective one of the work area outlets, and the second end of each of these horizontal cables is terminated into the IDCs of a respective one of the connector ports on the patch panel. In an “inter-connect” patching system, a single set of patch cords is used to directly connect the connector ports on a first set of patch panels to respective connector ports on network switches. In a “cross-connect” patching system, a second set of patch panels is provided, and the first set of patch cords is used to connect the connector ports on the first set of patch panels to respective connector ports on the second set of patch panels, and the second set of typically single-ended patch cords is used to connect the connector ports on the second set of patch panels to respective connector ports on the network switches. In both inter-connect and cross-connect patching systems the cascaded set of plugs, jacks and cable segments that connect a connector port on a network switch to a work area end device is typically referred to as a channel. Thus, if RJ-45 jacks are used as the connector ports, each channel includes four communications paths (since each jack and cable has four differential pairs of conductors).
The connections between the work area end devices and the network switches may need to be changed for a variety of reasons, including equipment changes, adding or deleting users, office moves, etc. In an inter-connect patching system, these connections are typically changed by rearranging the patch cords in the set of patch cords that run between the first set of patch panels and the network switches. In a cross-connect patching system, the connections between the work area end devices and the network switches are typically changed by rearranging the patch cords in the set of patch cords that run between the first set of patch panels and the second set of patch panels. Both types of patching systems allow a network manager to easily implement connectivity changes by simply unplugging one end of a patch cord from a first connector port on one of the patch panels in the first set of patch panels and then plugging that end of the patch cord into a second connector port on one of the patch panels in the first set of patch panels.
The connectivity between the connector ports on the network switches and the work area outlets is typically recorded in a computer-based log. Each time patching changes are made, this computer-based log is updated to reflect the new patching connections. Unfortunately, in practice technicians may neglect to update the log each and every time a change is made, and/or may make errors in logging changes. As such, the logs may not be complete and/or accurate.
In order to reduce or eliminate such logging errors, a variety of systems have been proposed that automatically log the patch cord connections in a communications patching system. These automated patching systems typically use special “intelligent” patch panels that employ sensors, radio frequency identification tags, serial ID chips and the like and/or special patch cords that include an additional conductor to detect patch cord insertions and removals and/or to automatically track patching connections. Typically, these systems require that all of the patch panels in the patching system have these automatic tracking capabilities and, in inter-connect systems, may also require that the network switches include automatic tracking capabilities as well.
The use of common mode signalling has also been explored as a means for automatically tracking patch cord connections in a communications patching system. As noted above, communications systems that use conductive wires as the cabling media typically transmit each communications signal as a differential signal. As known to those of skill in the art, differential signalling refers to a technique whereby an information signal is transmitted between devices over a pair of conductors rather than over a single conductor. With differential signalling, the signals transmitted on each conductor of the differential pair have equal magnitudes, but opposite phases, and the information signal is embedded as the voltage difference between the signals carried on the two conductors of the pair. Differential signalling is used because it can reduce the impact that external noise sources may have on the transmitted signal. In particular, when signals are transmitted over a tightly twisted differential pair of conductors, electrical noise from external sources will typically be picked up by each conductor of the pair in approximately equal amounts. As the information signal is extracted from the differential pair by taking the difference of the signals carried on the two conductors of the pair, the approximately equal amounts of noise that are picked up by each conductor cancel out in the subtraction process. As such, the use of differential signalling can reduce the impact of external noise sources on a transmitted signal.
In a communications system that includes multiple differential pairs per cable/connector, such as RJ-45 communications systems, “common mode” signalling may be used to transmit one or more additional signals over the cables and connectors. As known to those of skill in the art, a common mode signal refers to the part of a signal that is transmitted between devices over two (or more) conductors that is extracted from the transmitted signal by taking the voltage average of the signals carried on the two (or more) conductors. Theoretically, a common mode and a differential signal may be transmitted over a differential pair without interfering with each other. In particular, since the differential information signal is extracted from the differential pair by taking the difference between the signals carried by the two conductors of the pair, the common mode signal is theoretically removed by the subtraction process. Likewise, the differential signal does not theoretically interfere with the common mode signal as the differential signal adds equal but opposite signals that cancel out when the signals on each conductor of the pair are averaged to recover the common mode signal.
In a communications cable that includes multiple pairs of conductors, multiple common mode signals may be transmitted along with the differential signals. By way of example, in a communications cable that includes two differential pairs (four conductors total), a differential signal may be transmitted over each differential pair and a common mode signal may also be transmitted over each differential pair for a total of four transmitted information signals. Alternatively, the two common mode signals may be replaced with a third differential signal that is simultaneously transmitted over all four conductors. In particular, the third differential signal may be transmitted by transmitting its negative component as a common mode signal over both conductors of the first differential pair, and by transmitting its positive component as a common mode signal over both conductors of the second differential pair. As the transmission of the negative component of the third differential signal adds the exact same signal to each conductor of the first differential pair, the negative component of the third differential signal is effectively removed from the first differential pair during the subtraction process that is used to recover the first differential signal. The same is true for the positive component of the third differential signal that is transmitted over the second differential pair. Thus, in the above-described manner two differential pairs may be used to transmit a total of three differential signals. Although it cannot be characterized as a common mode signal, the third differential signal is comprised of two oppositely polarized common mode components, and thus it involves the use of common mode signalling. In order to distinguish signals such as the above-described third differential signal from both standard differential signals that are carried on two conductors and from true common mode signals, herein differential signals that are comprised of two oppositely polarized common mode components are referred to as “phantom mode” signals.
U.S. Pat. No. 7,573,254 to Cobb et al. (“the '254 patent”) discloses patch panels that include port identification circuits that transmit control signals over a phantom mode transmission path to track patch cord connections. In an embodiment disclosed in the '254 patent, a center tap inductor is used to inductively couple the phantom mode signal onto two of the differential pairs in a communications channel. U.S. Patent Publication No. 2010/0008482 to Tucker discloses techniques in which phantom mode signalling is used to discover the patch panel connector ports in first and second patching zones to which backbone cables are connected. U.S. Patent Application No. 2010/0244998 to Peyton et al. discloses injecting phantom mode signals onto a communications cable in order to determine interconnections within a local area network.